Conventional ceramic materials are used extensively in industry as engineered materials and products. They are very hard materials with good thermal resistance and corrosion resistance. They tend, however, to incorporate defects during formation processes, which lead to strength faults under specified temperature and pressure conditions. These materials, while they are very hard, are also very brittle. This results in splintering and cracking upon sudden or rapid loss in temperature, or upon impact with another material of high hardness.
A metal can be used to supplement conventional ceramic materials to compensate for a particular deficiency which hinders use of ceramic materials for a specified purpose. Such deficiencies might include brittleness, susceptibility to thermal shock and formation defects. Carefully selected metal components may cure one or several of these deficiencies. The resulting composite material will better withstand high temperature, and display less rigid and more ductile characteristics with less tendency to fracture when struck hard or cooled or heated rapidly.
Metal reinforced ceramic composites are well known and are important in the ceramic industry for high temperature engineering components, such as components in gas turbine and diesel engines, where rapid temperature change stability, high temperature strength, and creep resistance are necessary. Metal-ceramic composites generally possess high tensile strength, high thermal stability and high ductility. They differ from conventional ceramic materials in that they are much less brittle and are less prone to the formation of extended defects within the material than are conventional ceramics. Further, conventional ceramics do not have the compositional range of metal-ceramic composites. The addition of a metal alloy to the ceramic material adds both toughness and ductility, resulting in a metal-ceramic composite which can be conformed to a desired shape and is much tougher than the same item formed from conventional ceramic material. The degree to which a given metal-ceramic composite possesses given mechanical and physical properties is dependent on the exact elemental composition of that composite, as different elements contribute different properties in varying degrees. These materials are of special interest for use in applications requiring wear and corrosion resistance and high mechanical strength at high temperatures.
Known metal-ceramic compositions have thus far been limited to crystalline solids, and the development of such composites has been based on the performance characteristics of the crystalline components. These known composites are often synthesized by physically mixing the ceramic and metal components, or by depositing one component into a matrix of the other. Mohammad Ghouse has discussed the use of Ni-SiC crystalline composites as a coating on steel in "Influence of Heat Treatment on the Bond Strength of Codeposited Ni-SiC Composite Coatings," Surface Technology, 21 (1984), 193-200. Ghouse uses a heat treatment to bond the composite to the substrate after codeposition of the composite components.
M. Viswanathan et al., of the Indian Institute of Technology, reported on sediment codeposition involving nonmetallic particles being incorporated into a metal phase by keeping the nonmetallic particles in suspension by agitation in an electrolyte while the metal is deposited on a host surface. Metal Finishing, "Sediment Codeposition - A New Technique for Occlusion Plating," Vol. 70, 1972, pg. 83-84.
The use of metal-ceramic composites as coatings is discussed by F. N. Hubbell in the December, 1978 issue of Plating and Surface Finishing, pages 58-62, "Chemically Deposited Composites - A New Generation of Electroless Coatings," as well as by E. Broszeit, "Mechanical, Thermal and Tribological Properties of Electro - and Chemodeposited Composite Coatings," Thin Solid Films, 95 (1982), 133-142. These articles disclose metal-ceramic coating compositions and means of coating application.
Developments in the field of metal matrix composites, and needs not yet met are reported in the Journal of Metals, Mar. 1984, pages 19-25, "Developments in Titanium Metal Matrix Composites," by Smith and Froes. Hot isostatic pressing, and vacuum hot pressing are among the reported techniques for composite production. Here, as above, the composites disclosed are crystalline metal composites. Amorphous metal composites and microcrystalline metal composites are not contemplated by these disclosures.
Recently, however, amorphous metals have been given close scrutiny by the technical community due to their unique characteristics. They can be formulated to possess high compositional diversity due to the high free energy state of the initial components. Such compositional diversity makes possible incorporation of various characteristics and properties into the resultant material. The individual components selected will dictate what characteristics and properties are imparted to the amorphous metal. Amorphous metals are also highly resistant to corrosion and wear, and possess high mechanical strength and thermal stability, as well as ductility. These properties make amorphous metals prime candidates for use in metal-ceramic composites to compensate for ceramic material deficiencies.
Microcrystalline metals are also of interest for use in metal-ceramic composites. They possess high thermal stability, high tensile strength and high ductility, as well as being corrosion and wear resistant. The range of compositions which can be attained in microcrystalline formulations, in conjunction with the properties just mentioned, makes incorporation of microcrystalline metals into ceramic materials, to form a microcrystalline metal-ceramic composite, a desirable means for correction of ceramic material deficiencies.
What is lacking in the area of metal-ceramic composites is novel composites incorporating amorphous and microcrystalline metals and a simple process for the direct formation of a large variety of amorphous metal-ceramic and microcrystalline metal-ceramic compositions. Especially lacking is a simple process that would synthesize these novel metal-ceramic composites directly as powders which may undergo heat treatment to produce a desired shape or form without the attendant extended defects and brittleness associated with conventional ceramic materials that are not enhanced by metal components.
Hence, it is one object of the present invention to provide novel amorphous metal-ceramic composites and novel microcrystalline metal-ceramic composites.
It is another object of the present invention to provide a simple process for the preparation of a large variety of homogeneous amorphous metal-ceramic composites and microcrystalline metal-ceramic composites.
These and additional objects of the present invention will become apparent in the description of the invention and examples that follow.